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Cherlyn J Ng, Martin S Banks, Duje Tadin, Randolph Blake, Geunyoung Yoon; Can human stereopsis improve by making the eyes optically perfect?. Journal of Vision 2019;19(10):130b. doi: https://doi.org/10.1167/19.10.130b.
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Higher-order ocular aberrations (HOAs) limit visual acuity even when spherical and cylindrical errors are well corrected. We investigated how such aberrations affect stereoacuity. Four stereo-normal adults were tested psychophysically in a binocular adaptive-optics vision simulator. With this simulator, we can correct sphero-cylindrical and higher-order aberrations in real time. High-contrast visual acuity was measured with the “Tumbling E” method. Stereoacuity was measured with random-dot stereograms that portray sinusoidal depth corrugations (1, 2, or 3cpd). On average participants had 0.27±0.15μm RMS wavefront error for higher-order aberrations (HOAs). Full correction decreased this error to < 0.05μm, and significantly improved visual acuity in all participants (p< 0.01). The improvement in visual acuity was particularly large for a participant with large HOAs (0.54 RMS error; 0.218 vs 0.142±0.07logMAR). Stereo thresholds increased significantly and had greater variation between participants with increasing corrugation frequency (p< 0.01), but were significantly lower after HOA correction (27.30±17.16arcsec vs. 45.86±33.26; p=0.05). There were larger improvements at high frequencies that tended towards significance (1cpd: 1.8-, 2cpd: 2.5- and 2.3-fold improvement; p>0.1, p=0.1, p=0.07 respectively). There was no significant correlation between stereoacuity and the amount of correction for HOAs. Correcting higher-order aberrations produces consistent improvement in visual acuity, but stereo acuity was not correlated with HOAs. The lack of correlation suggests factors beyond optics that further limit performance to ceiling after correction. We suggest neural factors play a role, at least in part, with the smaller improvement on stereopsis at low frequencies being attributable to reliance on relatively large receptive fields required for computing binocular disparity.
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